The present invention relates to the processing of waste refinery sludge material in a delayed coking process.
Waste refinery sludge, having a high water content along with hydrocarbon liquids and solids present a difficult disposal problem. Such waste sludges may come from the API separator (used to separate water and hydrocarbons in refinery waste streams) and from backwashes from strainers in the bottom of the coker fractionator and blowdown tower. One approach has been to dispose of these sludges in the coking process. For example, in U.S. Pat. No. 4,666,585, sludge is fed into the coke drum via the heater transfer line. The sludge is mixed with the coke drum feed and then enters the coke drum. Water and the lighter hydrocarbons in the sludge are vaporized and leave the coke drum as an overhead vapor. The heavier hydrocarbon liquids and solids are mixed in the mesophase in the drum and react to form green coke.
Another variation is shown in U.S. Pat. No. 4,968,407 wherein the sludge is fed into the coker blowdown drum where it is mixed with coker blowdown oil and where water and the lighter hydrocarbons are recovered. The remaining sludge-oil mixture is then fed directly to the bottom of the coke drums via the transfer line either directly or through the fractionator and coker heater.
Sending the waste sludge containing solids to the coke drums through the transfer line and possibly also through the coker heater causes fouling and premature coking because this waste sludge is a more easily cokable material than the normal coker fresh feed.